1. Field of the Invention
The present invention relates to input apparatuses and manufacturing methods of the input apparatuses and particularly to an input apparatus including a sensor film having a two-dimensional or three-dimensional curved surface and a manufacturing method of the input apparatus.
2. Description of the Related Art
In information processing apparatuses, light-transmissive input apparatuses are disposed in front of display panels such as color liquid crystal panels. Such an input apparatus is referred to as a touch panel. In the touch panel, an electrostatic capacitance is formed between electrodes, and when a person's finger approaches, coordinates of the approach position of the finger is determined on the basis of a change of charge transfer. The change of charge transfer is detected by a capacitive sensor.
Recent years have seen the emergence of display apparatuses that display images on two-dimensional or three-dimensional curved surfaces. Display apparatuses having shapes corresponding to such curved display surfaces also need to be built in touch panels.
Japanese Unexamined Patent Application Publication No. 2009-130283 discloses an external case for an electronic apparatus provided with a sensor film having a three-dimensional curved surface. In the external case for an electronic apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2009-130283, a base formed of a synthetic resin is provided between a first film having predetermined color (coloring), pattern, or the like and a second film having an electrode portion and a conductive pattern.
Japanese Unexamined Patent Application Publication No. 2009-130283 further discloses a step in which, as a manufacturing method of the external case for an electronic apparatus, the first film and the second film are disposed in a die, a molten resin for forming the base is poured between the first film and the second film, and the molten resin is solidified so as to integrate the first film and the second film with the base. Japanese Unexamined Patent Application Publication No. 2009-130283 further discloses preforming by heating each film as a preceding step of disposing the first film and the second film in the die.
Japanese Unexamined Patent Application Publication No. 2013-246741 discloses a three-dimensional curved surface touch panel including a transparent base sheet, a main electrode layer formed by using conductive ink, and an auxiliary electrode layer formed by using conductive ink. The three-dimensional curved surface touch panel disclosed in Japanese Unexamined Patent Application Publication No. 2013-246741 is formed by disposing, in a die having a three-dimensional curved surface, a stack of three layers (the base sheet, the main electrode layer, and the auxiliary electrode layer) that have initially been flat and thermally softening the stack so as to deform the stack in accordance with the three-dimensional curved surface of the die.
However, it is difficult to locally control an extension portion of the sensor film in preforming or In-Mold Lamination (IML). Thus, an extension state of the sensor film depends on a total extension amount of the entire touch panel having a three-dimensional curved surface.
For example, even in a case in which a sufficiently gentle curved surface is provided in an area (detection area) in which a sensor is formed, if an area (non-detection area: a frame portion or the like) other than the area in which a sensor is formed includes a curved surface having a radius of curvature (minimum radius of curvature) smaller than a radius of curvature of the curved surface in the detection area, the total extension amount of the entire touch panel becomes relatively long. Accordingly, if a curved surface having the minimum radius curvature is present in the non-detection area, a tensile strength is generated by the extension of the non-detection area and might possibly affect the detection area in the sensor film in such a manner that the detection area extends more than an allowable extension amount and is destructed. Thus, the shape of a touch panel is restricted by the extension amount of the curved surface having the minimum radius of curvature.
As one of measures against this, a sensor film may be formed only in the detection area and may be excluded from the non-detection area. However, this measure allows an end portion of an object obtained by molding such as IML to remain in the touch panel so as to cross the touch panel. The end portion of the object obtained by molding such as IML is a portion where the constituent of material changes and is a portion where stresses applied to the touch panel are concentrated. If such a portion is present across the touch panel, the strength of the touch panel significantly decreases.